When capturing an image using an electronic device having a camera, the electronic device may display a preview image on a screen or display, capture the image indicated by the preview, and store the captured image. The electronic device may perform the aforementioned operation in a preview mode. A sleep mode may be utilized to conserve energy when not capturing an image. In the sleep mode, the electronic device may turn off the screen and enter the sleep mode from the preview mode. The sleep mode may be triggered when a input is not received from the user in the preview mode for a predetermined time. Alternatively, it may be triggered manually via a key input, activation of which causing the electronic device to enter the sleep mode from the preview mode. In the sleep mode, the electronic device turns off the screen, and thus electric power consumption is reduced. The electronic device may enter the preview mode from the sleep mode through a physical key input for entering the preview mode.